NAME

ctm_smail, ctm_dequeue, ctm_rmail — send and receive ctm(8) deltas via mail

SYNOPSIS

DESCRIPTION

In conjunction with the ctm(8) command, ctm_smail, ctm_dequeue and ctm_rmail are used to distribute changes to a source tree via email. The ctm_smail utility is given a compressed ctm delta, and a mailing list to send it to. It splits the delta into manageable pieces, encodes them as mail messages and sends them to the mailing list (optionally queued to spread the mail load). Each recipient uses ctm_rmail (either manually or automatically) to decode and reassemble the delta, and optionally call ctm to apply it to the source tree. At the moment, several source trees are distributed, and by several sites. These include the FreeBSD-current source and CVS trees, distributed by freefall.FreeBSD.org.

Command line arguments for ctm_smail:

-l log

Instead of appearing on stderr, error diagnostics and informational messages (other than command line errors) are time stamped and written to the file log.

-m maxmsgsize

Limit the maximum size mail message that ctm_smail is allowed to send. It is approximate since mail headers and other niceties are not counted in this limit. If not specified, it will default to 64000 bytes, leaving room for 1535 bytes of headers before the rumoured 64k mail limit.

-c maxctmsize

Limit the maximum size delta that will be sent. Deltas bigger that this limit will cause an apology mail message to be sent to the mailing list. This is to prevent massive changes overwhelming users' mail boxes. Note that this is the size before encoding. Encoding causes a 4/3 size increase before mail headers are added. If not specified, there is no limit.

-q queue-dir

Instead of mailing the delta pieces now, store them in the given directory to be mailed later using ctm_dequeue. This feature allows the mailing of large deltas to be spread out over hours or even days to limit the impact on recipients with limited network bandwidth or small mail spool areas.

ctm-delta is the delta to be sent, and mail-alias is the mailing list to send the delta to. The mail messages are sent using sendmail(8).

Command line arguments for ctm_dequeue:

-l log

Instead of appearing on stderr, error diagnostics and informational messages (other than command line errors) are time stamped and written to the file log.

-n numchunks

Limit the number of mail messages that ctm_dequeue will send per run. By default, ctm_dequeue will send one mail message per run.

queuedir is the directory containing the mail messages stored by ctm_smail. Up to numchunks mail messages will be sent in each run. The recipient mailing list is already encoded in the queued files.

It is safe to run ctm_dequeue while ctm_smail is adding entries to the queue, or even to run ctm_smail multiple times concurrently, but a separate queue directory should be used for each tree being distributed. This is because entries are served in alphabetical order, and one tree will be unfairly serviced before any others, based on the delta names, not delta creation times.

Command line arguments for ctm_rmail:

-l log

Instead of appearing on stderr, error diagnostics and informational messages (other than command line errors) are time stamped and written to the file log.

-p piecedir

Collect pieces of deltas in this directory. Each piece corresponds to a single mail message. Pieces are removed when complete deltas are built. If this flag is not given, no input files will be read, but completed deltas may still be applied with ctm if the -b flag is given.

-d deltadir

Collect completed deltas in this directory. Deltas are built from one or more pieces when all pieces are present.

-b basedir

Apply any completed deltas to this source tree. If this flag is not given, deltas will be stored, but not applied. The user may then apply the deltas manually, or by using ctm_rmail without the -p flag. Deltas will not be applied if they do not match the .ctm_status file in basedir (or if .ctm_status does not exist).

-B backup_dir

Specify a backup directory for use by ctm -B

-D

Delete deltas after successful application by ctm. It is probably a good idea to avoid this flag (and keep all the deltas) as ctm has the ability to recover small groups of files from a full set of deltas.

-f

Fork and execute in the background while applying deltas with ctm. This is useful when automatically invoking ctm_rmail from sendmail because ctm can take a very long time to complete, causing other people's mail to be delayed, and can in theory cause spurious mail retransmission due to the remote sendmail timing out, or even termination of ctm_rmail by mail filters such as MH's slocal. Do not worry about zillions of background ctm processes loading your machine, since locking is used to prevent more than one ctm invocation at a time.

-u

Pass the -u flag to the ctm command when applying the complete deltas, causing it to set the modification time of created and modified files to the CTM delta creation time.

-v

Pass the -v flag to the ctm command when applying the complete deltas, causing a more informative output. All ctm output appears in the ctm_rmail log file.

The file arguments (or stdin, if there are none) are scanned for delta pieces. Multiple delta pieces can be read from a single file, so an entire maildrop can be scanned and processed with a single command.

It is safe to invoke ctm_rmail multiple times concurrently (with different input files), as might happen when sendmail is delivering mail asynchronously. This is because locking is used to keep things orderly.

FILE FORMAT

Following are the important parts of an actual (very small) delta piece:

From: owner-src-cur
To: src-cur
Subject: ctm-mail src-cur.0003.gz 1/4

CTM_MAIL BEGIN src-cur.0003.gz 1 4
H4sIAAAAAAACA3VU72/bNhD9bP0VByQoEiyRSZEUSQP9kKTeYCR2gDTdsGFAwB/HRogtG5K8NCj6
v4+UZSdtUQh6Rz0eee/xaF/dzx8up3/MFlDkBNrGnbttAwyo1pxoRgoiBNX/QJ5d3c9/X8DcPGGo
lggkPiXngE4W1gUjKPJCYyk5MZRbIqmNW/ASglIFcdwIzTUxaAqhnCPcBqloKEkJVNDMF0Azk+Bo
dDzzk0Ods/+A5gXv9YyJHjMCtJwQNeESNma7hOmXDRxn
CTM_MAIL END 61065

The subject of the message always begins with “ctm-mail” followed by the name of the delta, which piece this is, and how many total pieces there are. The data are bracketed by “CTM_MAIL BEGIN” and “CTM_MAIL END” lines, duplicating the information in the subject line, plus a simple checksum.

If the delta exceeds maxctmsize, then a message like this will be received instead:

From: owner-src-cur
To: src-cur
Subject: ctm-notice src-cur.0999.gz

src-cur.0999.gz is 792843 bytes.  The limit is 300000 bytes.

You can retrieve this delta via ftp.

You are then on your own!

ENVIRONMENT

If deltas are to be applied then ctm(8) and gunzip(1) must be in your PATH.

FILES

QUEUEDIR/*

Pieces of deltas encoded as mail messages waiting to be sent to the mailing list.

PIECEDIR/*

Pieces of deltas waiting for the rest to arrive.

DELTADIR/*

Completed deltas.

BASEDIR/.ctm_status

File containing the name and number of the next delta to be applied to this source tree.

EXIT STATUS

The ctm_smail, ctm_dequeue and ctm_rmail utilities return exit status 0 for success, and 1 for various failures. The ctm_rmail utility is expected to be called from a mail transfer program, and thus signals failure only when the input mail message should be bounced (preferably into your regular maildrop, not back to the sender). In short, failure to apply a completed delta with ctm is not considered an error important enough to bounce the mail, and ctm_rmail returns an exit status of 0.

EXAMPLES

To send delta 32 of src-cur to a group of wonderful code hackers known to sendmail as src-guys, limiting the mail size to roughly 60000 bytes, you could use:

ctm_smail -m 60000 /wherever/it/is/src-cur.0032.gz src-guys

To decode every ctm-mail message in your mailbox, assemble them into complete deltas, then apply any deltas built or lying around, you could use:

ctm_rmail -p ~/pieces -d ~/deltas -b /usr/ctm-src-cur $MAIL

(Note that no messages are deleted by ctm_rmail. Any mail reader could be used for that purpose.)

To create a mail alias called receiver-dude that will automatically decode and assemble deltas, but not apply them, you could put the following lines in your /etc/mail/aliases file (assuming the /ctm/tmp and /ctm/deltas directories and /ctm/log file are writable by user daemon or group wheel):

receiver-dude: "|ctm_rmail -p /ctm/tmp -d /ctm/deltas -l /ctm/log"
owner-receiver-dude: real_dude@wherever.you.like

The second line will catch failures and drop them into your regular mailbox, or wherever else you like.

To apply all the deltas collected, and delete those applied, you could use:

ctm_rmail -D -d /ctm/deltas -b /ctm/src-cur -l /ctm/apply.log

For maximum flexibility, consider this excerpt from a procmail script:

PATH=$HOME/bin:$PATH

:0 w
* ^Subject: ctm-mail cvs-cur
| ctm_incoming

together with the shell script ~/bin/ctm_incoming:

#! /bin/sh
PATH="$HOME/bin:/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin"
export PATH

cd $HOME/ctm && ctm_rmail -f -p pieces -d deltas -l log -b /ctm

which will deposit all ctm deltas in ~/ctm/deltas, apply them to the tree in /ctm, and drop any failures into your regular mail box. Note the PATH manipulation in ctm_incoming which allows ctm_rmail to execute ctm(8) on the (non-FreeBSD) machine that this example was taken from.

SECURITY

On its own, CTM is an insecure protocol - there is no authentication performed that the changes applied to the source code were sent by a trusted party, and so care should be taken if the CTM deltas are obtained via an unauthenticated medium such as regular email. It is a relatively simple matter for an attacker to forge a CTM delta to replace or precede the legitimate one and insert malicious code into your source tree. If the legitimate delta is somehow prevented from arriving, this will go unnoticed until a later delta attempts to touch the same file, at which point the MD5 checksum will fail.

To remedy this insecurity, CTM delta pieces generated by FreeBSD.org are cryptographically signed in a format compatible with the GNU Privacy Guard utility, available in /usr/ports/security/gpg, and the Pretty Good Privacy v5 utility, /usr/ports/security/pgp5. The relevant public key can be obtained by fingering ctm@FreeBSD.org.

CTM deltas which are thus signed cannot be undetectably altered by an attacker. Therefore it is recommended that you make use of GPG or PGP5 to verify the signatures if you receive your CTM deltas via email.

DIAGNOSTICS

In normal operation, ctm_smail will report messages like:

ctm_smail: src-cur.0250.gz 1/2 sent to src-guys

or, if queueing,

ctm_smail: src-cur.0250.gz 1/2 queued for src-guys

The ctm_dequeue utility will report messages like:

ctm_dequeue: src-cur.0250.gz 1/2 sent

The ctm_rmail utility will report messages like:

ctm_rmail: src-cur.0250.gz 1/2 stored
ctm_rmail: src-cur.0250.gz 2/2 stored
ctm_rmail: src-cur.0250.gz complete

If any of the input files do not contain a valid delta piece, ctm_rmail will report:

ctm_rmail: message contains no delta

and return an exit status of 1. You can use this to redirect wayward messages back into your real mailbox if your mail filter goes wonky.

These messages go to stderr or to the log file. Messages from ctm(8) turn up here too. Error messages should be self explanatory.

SEE ALSO

ctm(5), ctm(8)

AUTHORS

Stephen McKay <mckay@FreeBSD.org>